1. Field of the Invention
The present invention relates to a light emitting device having an element which sandwiches light emitting material between electrodes and an electric appliance which uses such a light emitting device as a display part (display or display monitor), and more particularly to a light emitting device which uses light emitting material which can obtain EL (Electro Luminescence) (called EL material hereinafter). Here, an organic EL display and an organic light emitting diode (OLED: Organic Light Emitting Diode) are included in the light emitting device of the present invention.
Further, the EL material applicable to the present invention includes all EL materials which emit light (phosphorus light and/or fluorescence) through a singlet excitation or a triplet excitation or both excitations.
2. Related Art
Recently, the development of light emitting devices which use self luminous elements (called EL elements hereinafter) making use of an EL phenomenon of EL material (called EL light emitting device hereinafter) has been in progress. Since the EL light emitting device is a display device which uses the self luminous elements, the EL light emitting devices do not require back lights such as liquid crystal displays and have a large angle of visibility. Accordingly, the EL light emitting devices are attracting attentions as a display part of a portable equipment which can be used outside.
There exist two types of EL light emitting devices, that is, a passive matrix type and an active matrix type and both of them have been widely developed. Particularly, recently, the EL light emitting devices of active matrix type have been attracting attentions. The EL light emitting device of active matrix type is characterized in that thin film transistors (called TFT hereinafter) are provided to respective pixels which constitute a pixel portion and an electric current quantity supplied to the EL elements is controlled by the TFT.
An advantage of the active matrix type lies in the image display of high definition which can provide images of a larger information quantity.
However, since respective pixels require the TFTs, the fabrication process becomes complicated compared to that of the passive matrix type so that there arise problems such as the lowering of yield and the increase of fabrication cost due to the prolonged fabrication period. Particularly, when there are many photolithography steps, the lowering of the yield becomes apparent so that the reduction of the photolithography steps has been a crucial task to be solved.
The present invention has been made in view of the above and it is an object of the present invention to provide an inexpensive light emitting device by reducing the fabrication cost which is brought about by the enhancement of the yield and the shortening the fabrication period derived from the reduction of photolithography steps. Further, it is another object of the present invention to provide an inexpensive electric appliance which uses an inexpensive light emitting device as a display part thereof.